This invention is directed to the recirculation of gas in carbon dioxide lasers, and in particular to a recirculating system which reduces the gas requirements by removing oxygen produced from the dissociation of carbon dioxide.
In carbon dioxide lasers which include mixtures of CO.sub.2, N.sub.2 and He, the dissociation of CO.sub.2 into CO and atomic oxygen occurs and can result in degeneration of the uniform glow discharge, necessary for laser excitation, into an arc either directly, or through the production of detrimental species such as oxides of nitrogen. Several techniques have been developed to control the gas chemistry in TE CO.sub.2 lasers such that steady-state operation may be achieved. One technique consists of including gas additives such as H.sub.2 and CO in controlled amounts in the initial gas mixture, as described in the publication by P. N. Pace et al. in the IEEE Journal, QE, Vol. QE-14, No. 4, pp. 263-274, 1978. Another technique consists of using a catalyst in the gas loop of the laser to combine the carbon monoxide with the oxygen, as described in the publication by C. Willis et al. Applied Physics Letters, Vol. 31, No. 2, pp. 84-86, 1977.
These methods have proved effective in reducing the fuel gas requirements in TEA CO.sub.2 lasers under a range of conditions, notably operation at or near one atmosphere and at relatively modest electrical input energy density. During the 1979 IEEE/OSA Conference on Laser Engineering and Applications held in Washington, D.C., May 30-June 1, 1979, H. Nagai et al. mentioned the use of a moisture adsorbent in a cw CO.sub.2 laser in order to exclude H.sub.2 O in the laser.
Under more extreme operating conditions, these techniques are no longer satisfactory, particularly in operation at pressures substantially in excess of one atmosphere. At higher pressure, the effectiveness of ultraviolet preionization is reduced due to absorption of this radiation in CO.sub.2. Thus, the stability of the discharge, which is critically dependent on the number density of electrons produced by this radiation, is reduced and becomes more sensitive to the detrimental effects of gaseous discharge products. This in turn leads to a large input gas flow, particularly for repetitively pulsed operation, to ensure that the detrimental species are maintained below some critical concentration.